1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery capable of improving bonding power between a molded resin member and an upper part of a bare cell to improve the adhesion of a protection circuit board and a secondary protection element to the bare cell.
2. Description of Related Art
In general, with a reduction in the sizes and an improvement in the performance of portable wireless apparatuses, such as video cameras, mobile phones, and notebook computers, numerous researches on secondary batteries used as power sources for the portable wireless apparatuses have been made. Such secondary batteries include, for example, a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-zinc battery, and a lithium secondary battery. Among them, the lithium secondary battery that is rechargeable and can be made in a small size with a high capacity has come into widespread use in the field of high-tech electronic apparatuses due to its advantages such as high operation voltage and high energy density per unit weight.
In the lithium secondary battery, an electrode assembly including a positive electrode plate, a negative electrode plate, and a separator is put into a metal can, an electrolyte is injected into the can, and the can is sealed up, thereby forming a bare cell. In general, the bare cell has an electrode terminal insulated from the can at an upper part thereof. The electrode terminal has a positive or negative polarity of the lithium secondary battery, and the can has the other polarity. Therefore, the positive electrode plate of the electrode assembly is connected to one of the can and the electrode terminal, and the negative electrode plate is connected to the other of the can and the electrode terminal.
A safety device, such as a protecting circuit module (PCM) including a protection circuit board and a secondary protection element, such as a positive temperature coefficient (PTC) element or bimetal, is connected to the top or the side of the sealed bare cell, and the bare cell having the safety device connected thereto is put into a battery pack, or it is molded with resin to form a lithium secondary battery. In this case, the safety devices of the lithium secondary battery are connected respectively to a positive electrode and a negative electrode to break a current when the voltage of the battery is suddenly increased due to the overheat or over discharge of the battery, thereby preventing the explosion of the battery.
In general, in the secondary batteries, the bare cell, protection circuit board and other battery parts are fixed by the molded resin member to form a battery pack.
The molded resin member, however, is not formed of the same material as that forming the bare cell including the cap plate and the can that is made of a metallic material, and the contact area between the molded resin member and the bare cell is small, which results in low adhesion. As a result, the molded resin member is not kept at its normal position on the bare cell, and is distorted or detached from the bare cell.